Electrosurgery has been performed since the end of the nineteenth century and involves the use of the high frequency current to cut or coagulate tissue with an active electrode. A return electrode is placed in contact with the patient while a surgeon brings the active electrode either in contact with or adjacent to a body tissue. The high frequency current generates heat in the tissue, diathermy, which cuts the tissue and causes desiccation, the coagulation resulting in elongated cells shrunken by dehydration. By adjusting the current used, it is possible to cut tissue as with a knife or to coagulate the tissue to stop bleeding with or without also cutting the tissue.
In use, the large return electrode is positioned in contact with the body of the patient and connected to an electrosurgical power source. The electrosurgical power source produces a high frequency current in excess of 10,000 Hz with a preferred frequency being between 0.5 and 5 MHz. An undamped continuous sinusoidal waveform is best for strictly cutting tissue while a series of damped sinusoidal waves have been found best to achieve coagulation. Cutting with hemostasis is usually accomplished by using some combination of these waveforms.
As the small active electrode is brought into contact or close proximity with a body tissue the current at the tip of the electrode is concentrated over a small area giving a high current density, which coupled with the local electrical resistance of the tissue provides the effects necessary for cutting or coagulation. Heat is produced by the resistance to current flow as the electrical energy is absorbed and converted into thermal energy. The exact mechanisms and manner in which the area surrounding the active electrode heats, leading to a cutting effect, are not well understood at present and research is under way to better explain these phenomena.
At the tip of the electrode the current density and resistance are at their maximum, generating enough heat in a tissue for vaporization and pyrolysis. As the current spreads out through the body it is conducted over a much larger surface area, reducing the effective resistance and current density, and no significant heating occurs. The current completes its path back to the electrosurgery unit via the return electrode, also called the patient plate or dispersive electrode. This electrode always has a large surface area and is coated with an electrode paste to keep a low current density and resistance, thus avoiding areas of local heating and possible burns to the patient as the current leaves the body.
Electrosurgery is particularly useful when operating on highly vascularized tissue such as liver or muscle. Certain specialized uses for electrosurgery are so well established that they have become the standard technique, as in transurethral resection of the prostate and certain intracranial cutting procedures. However, the heat generated by electrosurgery produces much smoke distracting the surgeon and making it difficult for him to see what he is doing. Accordingly it becomes necessary to have an assistant present to blow away or aspirate the undesirable smoke. While such aid makes it possible for the operating surgeon to see, the necessity of either removing smoke or providing a light source distracts the operating surgeon and can result in the loss of concentration.
Accordingly it is desirable to provide an electrosurgery instrument which would improve the vision of the operating surgeon by removing the smoke and possibly also providing a local light source. It is also desirable that such an instrument be compact and easy to use without distracting the surgeon.